The time in a girl's life that menstruation first begins. During the menarche period, menstruation may be irregular and unpredictable. Mood, weight, activity level, and growth rate may fluctuate with the hormone levels as well. Synonymous with female puberty.

the start of the menstrual periods and other physical and mental changes associated with puberty. The menarche occurs when the reproductive organs become functionally active and may take place at any time between 10 and 18 years of age. Comparegonadarche.

menarche — noun /mɛˈnɑːki/ The onset of menstruation; the beginning of the menstrual period. A girls first period. How old is she? Nine? Ten? The menarche is not far off – a hint of a bosom, poor child. Ant: menopause … Wiktionary

menarche — n. the start of the menstrual periods and other physical and mental changes associated with puberty. The menarche occurs when the reproductive organs become functionally active and may take place at any time between 10 and 18 years of age.… … The new mediacal dictionary

menarche — noun Etymology: New Latin, from men + Greek archē beginning Date: circa 1900 the beginning of the menstrual function; especially the first menstrual period of an individual • menarcheal adjective … New Collegiate Dictionary